4" 9kW Stripping and Rectification

[tommysb]

I've been working on this column, various parts for the past year, maybe more. I have to say, just like my first 4" stripping column experiments, (2024) viewtopic.php?t=92203, and first attempt at something contiuous (2022) viewtopic.php?t=87493, I could only have done this with the help of this forum. Particularly Bolverk. This would have been impossible without him. So I'm going to try and share what I've learned in this process to help anyone else along!

Back around May this year Bolverk and I started throwing ideas back and forth. I was building a 4" stripper, and we started to discuss stuff via DM. We've done quite a few things that have/haven't worked. I was able to test some ideas, when he didn't have build time, and now he's got his column going (just about), we are trying to work out which design choices work and which don't. I am going to highlight key learnings which I think I found out during this process.

A very rough timeline of this still's progress would be something like -

January - Had a stripping column, packed with clay balls, driven by steam. Steam was generated in a 50l Kettle with triclamp and an element, and entered the column at the bottom via a one-way valve (essentially an inverted ubend into the bottom of the column.

April/May - Added an exeternal steam gen, a-la bolverk. Was still using clay balls in the column. Steam gen used a mechanical float valve. Kind of worked.
*takeaway* - use an external steam gen.

I recall making a flour wash, I think just with bakers' flour and enzymes. It separated into a flourly sludge at the bottom, and clear wash at the top. The clear wash ran really nicely, the floury sludge wouldn't go through the narrow bore or some of the fine bore heat exchange coils. I realised (but STILL haven't got this completely nailed), that if we want to run flour washes 'on the grain', that we need to keep the mix homogeneous. *takeaway* you need to keep flour washes homogeneous to run in these systems (but Telluride on SD already pointed this out in 2017 or so, I am just confirming with my experimental results!)

June/July - Moved to using stripping plates. Way better than balls. I think the first design was just a perf plate with various sections blanked off, and the current design has a downcomer. This made a huge difference. *takeaway* - don't bother with packing in these stills. Plates just work better, and there's a reason they do it in industry.

I think at this point the column was running fairly well aside from a couple of issues -

The float valve in the steam gen was failing (I got through 3 of them).
Foaming issues with some of the washes.

For the float valve - the failure mode was as follows:
Pressure in my steam-gen was getting higher than the water supply-line pressure, and cool water was not entering the system. This is caused by having a very low water pressure in the building, and also a very thin steam hose outlet. Water doesn't enter, valve heats up, valve fails. Even after system cooling down, now water doesn't enter well, etc etc.

The solution - change to electronic control in the steam gen. a 3-pin probe connected to a floatless level switch, used to control a supply solenoid (normally closed). Additionally, I have an external pump with a pressure bladder, to ensure a minimum supply pressure into the steam gen. *takeaway* use electronic control on your steam gen.

As for the foaming issues - I believe it's caused by residual sugars in the wort. Evidence for this is that I had terrible foaming issues with a high-gravity single malt wash, which finished with a high residual gravity around 1.010. Foamed like hell. I ran out of antifoam around this time, so wan't able to dose that in. (This was just a wort, no solids in, so classic beer mash protocol wish sparging off the grain).

Went back, and added some extraneous enzymes, watered down to reduce gravity, and added an aggressive yeast (champagne, sacc. bayanus). A new 5L bottle of antifoam arrived in the meantime. The wash finished bone-dry, and when I ran this, I had no issues with foaming.

I THINK the antifoam is not strictly necessary, if you have a good wash which finishes dry. I will however continue to use it, just to keep my life easier.

*takeaway* Make sure your wort is fermented dry.

So at this point, I had a stripping column with plates, that was able to process wash. I was stripping my single malt wash, then pot-stilling the low-wines. Kind of worked, BUT, I needed something more efficient. This is in use in a commercial distillery, which I try to run on the side of having a day-job, so any timesaver is a really really big deal to me.

Was chatting this through with Bolverk, and he convinced me to build a side column for this.

I didn't have parts for a 4" side column, but i had enough bits and pieces lying around to build a 2" column on top of my 50L boiler. I rigged that up, and I think first runs I couldn't get it to work. In Mid July, I was using this setup to strip, just not switching on any condensing in the spirit column and letting the vapour pass all the way through the system.
Stripping on a dual column 2" column



Continuous on 2" side starting to work.
*takeaway* You can run a smaller spirit column than your stripping column.

There were a few things I didn't like about this 2" design. Mostly, it was mechanical. It wasn't stable, and having good condensors etc isn't nice on a thin, tall column. The plates in it were only perf plates (they help up well, and actually I think a 2" perf works well in this situation), and liquid draw-off was via an LM-type cup, that only captured liquid from the edges of the column.

I felt I was not catching enough falling liquid, and too much was exiting in the spirit column 'tails'. On top of that, the proof coming out was not where I wanted it.

Just as we started to get this to work, around August 2025, we opened the distillery taproom/bar at this point, and progress completely stalled, as all my free time suddenly disappeared.

Fast forward to now, and a shitty landlord and a leaky roof meant that we had to close the taproom earlier this month. The upshot of this, is that I get a bit more time to work on the distillation side of things!

I had some parts that were sitting around waiting for this. A proper 4" column base, and some 4" spool with a 1/2" takeoff.

I decided to rebuild the column in 4" and see how she runs.

As for the plates, Bolverk and I had been discussing separate take-off and separation plates. My problem, is that I didn't have anything that would work well as a takeoff plate, and I am also impatient, and only had a small window for testing this stuff.

WhatsApp Image 2025-12-22 at 11.00.16.jpeg

The workaround to my impatience was to use a Procap with an extended downcomer. This keeps a higher liquid level on the plate, which will allow it to be drawn off through a ball valve attached on the 1/2" opening.

Last night, I managed to put everything together, and do a preliminary run.

Lo and behold, it kind of worked!



This wasn't a perfect test, for a couple of reasons.

1. I wasn't worrying about making proper (heads) cuts. I just wanted to make sure that I theoretically could knock down everything if I wanted to, and generally to test the liquid takeoff. So I ran the column completely as LM, with full water flow to the heads dephleg condensor, which consisted of a 4" dephleg stacked with a 3" shotgun (adding a lot of height to this all). I was able to knock down all vapor with this, and so everything going up or down the column was just taken off from the product draws.

In 'real' use, I would control the flow to these dephlegs, to allow a heads cut to be made. The vapor that passes the dephlegs will go through a separate product condensor, which I didn't implement yet as it was going to mean rigging up just more stuff, and more weight, etc etc.

2. The spirit I was running had already had a heads cut on it. I had some spirit from another previous continuous test, which I couldn't get the proof high enough. It was about 40%, and I had tried to cut heads on it. I proofed this down to about 8% with water, and was testing the column with this. An easy test to start, I suppose.

A couple of issues i encountered:

1. Not letting the plates load properly before takeoff meant that the bottom plate wasn't operational at first. This is easily overcome by just waiting a bit longer before opening my product valves. Like I said earlier, I am impatient.

2. This happened twice and is a big deal - The pressure in the bottom of the spirit column was enough to push all the liquid out of the vapor lock. I think a higher vapor lock would be part of the solution, but also, need to think about resistances and pressure etc in the column and check that everything is flowing up and down as it should. When this blows out, it's not good, as you're venting out a lot of alcohol vapor at kind of high proof (40-50%?).

It might be that when I also vent heads, this behaviour goes away. I am really not sure quite what causes it, and would really like to avoid it in future!

I gotta go put a mash on this evening, and hopefully have some wash to run later in the week. I have some Kveik yeast and think that I can mash, cool, and pitch at 40c, and it'll be done in 3-4 days. In the meantime, I will try and work out the heads cuts condensors, and the vapor lock issue.

over and out for now!